The Argentina winger has battled for minutes under Ranieri since the coach's appointment.
But he insists: "I believe in him a lot, I think he is a player for the future of Roma, he is improving in the aspect I ask of him, being more practical and touching the ball less. He will definitely stay with us because I believe in him a lot."
On Tommaso Baldanzi's future, he said: "At the moment I prefer him to Soulé because last year he had six months of adaptation. He gives the energy that I lack, he is another boy that I hold in high regard."
Asked if Lorenzo Pellegrini could leave Roma in January, Ranieri added: "Everything is possible in football but honestly I don't think he'll leave. If a team comes and he's happy to go... But it's the same for him as for everyone, honestly I don't think he'll leave, but it's my feeling."